While the meatballs are baking, heat olive oil over medium heat in a small sauce pan. Add the garlic and saute for 1 minute. Add in the cornstarch and mix (this will soak up the oil in the pan), and immediately add the milk. Bring to a boil, add the cinnamon, and reduce heat to low. Simmer for 2 minutes, stirring frequently. Remove from heat and add in the pumpkin, nutritional yeast (if using), salt and brown sugar.